1. Field of the Invention
The present invention relates to a heating device for heating a substrate coated with a film, such as a resist film, a heating method, a coating and developing system using the heating device, and a storage medium storing a computer program specifying steps of the heating method.
2. Description of the Related Art
A coating and developing system is used as a resist pattern forming system for forming a resist pattern on a semiconductor wafer (hereinafter, referred to simply as “wafer”) or a glass substrate for a LCD (liquid crystal display). The coating and developing system coats a wafer with a resist film, and develops a resist pattern after the wafer has been processed by an exposure process. The coating and developing system is internally provided with a heating device called a baking device. The heating device heats a wafer coated with a resist solution film to vaporize a solvent contained in the resist solution film to form a dry resist film on the wafer.
For example, when a resist film of a chemically amplified resist solution is exposed, an acid is produced in the resist film. The acid is diffused in the resist film by a heating process called a postexposure baking process (PEB process). Then, the wafer is cooled by a cooling process to stop the diffusion of the acid to form pats soluble in a developer and those insoluble in the developer in the resist film. It is possible that the width of lines forming the developed resist pattern becomes irregular unless the wafer is processed by the PEB process and the cooling process in a satisfactory intrasurface uniformity.
The coating and developing system is provided with a main arm for carrying a wafer in the coating and developing system, and the heating device is provided with a special arm having a cooling function to carry a wafer to and from a heating chamber of the heating device. The special arm places a wafer on a heating plate placed in the heating chamber. The special arm takes up a wafer processed by the heating process and can uniformly cool the wafer. Consequently, an accurate resist pattern can be formed.
The heating device of this type needs lifting pins and a lifting mechanism for lifting the lifting pins to transfer a wafer between the special arm and the heating plates, and to ensure a clearance for a transfer operation. Therefore, the heating device cannot be formed in a low height. Thus the heating device places a restriction on forming the coating and developing system in a layered structure to improve throughput. Time needed for transferring a wafer between the special arm and the heating plate is an overhead, namely, time that does not directly contribute to the heating process, causing the reduction of throughput.
To solve such a problem in the conventional heating device, the inventors of the present invention developed a heating device including a heating chamber, a cooling plate disposed in front of the heating chamber, and a wire for carrying a wafer between the cooling plate and the heating chamber. FIG. 16 is a typical cross sectional view of the interior of such a heating device 100. The heating device 100 is internally provided with a heating chamber 101 having the shape of a flat box provided with an opening 101a in its side wall, and a cooling plate 105 disposed in front of the heating chamber 101. The cooling plate 105 cools a wafer W processed by a heating process.
A wafer W carried into the heating device 100 is placed on the cooling plate 105 by an external wafer carrying mechanism as shown in FIG. 16A. The cooling plate 105 is provided with, for example, two grooves 105a extending in a direction perpendicular to a carrying direction in which the wafer W is carried. Two wires 104A and 104B are extended in the grooves 105a, respectively. The cooling plate 105 is lowered to transfer the wafer W to the wires 104A and 104B. A moving mechanism, not shown, interlocked with a wire-holding part holding the wires 104A and 104B moves the wires 104A and 104B to carry the wafer W through the opening 101a into the heating chamber 101.
The interior of the heating chamber 101 is heated beforehand by heating plates 102A and 102B disposed on and beneath the heating chamber 101, respectively. As shown in FIG. 16B, a hot gas is blown by a gas blowing device 103a, and the hot gas is sucked by an exhaust device 103b to produce a unidirectional flow of the hot gas. Thus the wafer W not placed in contact with the heating plate is heated. The wafer W thus heated is moved in the reverse direction toward the cooling plate 105, and is placed on the cooling plate 105 to cool the wafer W is cooled rapidly to stop changes in a resist film formed on the wafer W. The wafer W thus cooled is sent out from the heating device 100.
The heating device 100 of this type developed by the inventors of the present invention subjects the wafer W supported on the wires 104A and 104B to the heating process. Therefore, any operations like those needed by the conventional heating device for transferring a wafer W between the special arm and the heating plate are not necessary. Consequently, overhead time can be curtailed to prevent the reduction of throughput.
In this heating device 100, the wafer W is carried horizontally in a carrying direction into the heating chamber 101 heated beforehand. Therefore, there is a time difference in the range of about 1 to about 3 s between the time the front end, with respect to the carrying direction, of the wafer W enters the heating chamber 101 and the time the rear end, with respect to the carrying direction, of the wafer W enters the heating chamber 101. Consequently, there is an initial temperature distribution in the surface of the wafer W immediately after the wafer W has been completely inserted into the heating chamber 101, in which a temperature difference between the front and the rear end of the surface of the wafer W is, for example, about 3° C.
When the wafer W having the surface in which temperature is distributed in such an initial temperature distribution is processed by the PEB process, It is possible that parts of the resist film respectively corresponding to the front and the rear end of the wafer W are heated differently and, for example, lines of parts of a resist pattern respectively corresponding to the front and the rear end of the wafer W are formed in different widths, respectively.
Heating devices mentioned in Paragraph 0053 of JP-A H7-183291 (Cited reference 1) and in Paragraphs 0019 to 0021 of JP-A H100256170 (Cited reference 2) use heating lamps for heating a wafer. A technique mentioned in Cited reference 1 is intended for heating a substrate with heating lamps to prevent dew condensation in a heating chamber. A technique mentioned in Cited reference 2 is intended for improving the efficiency of heating a substrate with heating lamps. Thus those previously proposed techniques are different from the present invention intended to solve the foregoing problem resulting from the initial temperature distribution, and neither of those techniques is not applicable to solving the problem intended to be solved by the present invention.